U.S. patent number 6,712,904 [Application Number 09/937,107] was granted by the patent office on 2004-03-30 for device for producing single crystals.
This patent grant is currently assigned to Forschungszentrum Julich GmbH, Frieberger Compound Materials GmbH. Invention is credited to Thomas Bunger, Tilo Flade, Eckhard Kussel, Klaus Sonnenberg, Berndt Weinert.
United States Patent |
6,712,904 |
Sonnenberg , et al. |
March 30, 2004 |
**Please see images for:
( Certificate of Correction ) ** |
Device for producing single crystals
Abstract
A device is made available for producing monocrystals, for
example large-diameter gallium arsenide monocrystals, that has a
cylindrical heating appliance with a floor heater (2) and a cover
heater (3). The heating surfaces of the floor and the cover heater
are considerably larger than the cross-sectional area of the
monocrystal to be produced. In addition, an insulator (6) is
planned for the reaction space that is designed to prevent a radial
heat flow and the guarantee a strictly axial heat flow over the
complete height of the reaction space between the cover heater (3)
and the floor heater (2).
Inventors: |
Sonnenberg; Klaus (Niederzier,
DE), Kussel; Eckhard (Duren, DE), Bunger;
Thomas (Chemnitz, DE), Flade; Tilo (Freiberg,
DE), Weinert; Berndt (Freiberg, DE) |
Assignee: |
Forschungszentrum Julich GmbH
(Julich, DE)
Frieberger Compound Materials GmbH (Frieberg,
DE)
|
Family
ID: |
7901693 |
Appl.
No.: |
09/937,107 |
Filed: |
September 19, 2001 |
PCT
Filed: |
March 16, 2000 |
PCT No.: |
PCT/EP00/02349 |
PCT
Pub. No.: |
WO00/56954 |
PCT
Pub. Date: |
September 28, 2000 |
Foreign Application Priority Data
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Mar 19, 1999 [DE] |
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199 12 484 |
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Current U.S.
Class: |
117/222; 117/217;
117/219; 117/83; 164/122; 164/122.1; 164/122.2; 164/123 |
Current CPC
Class: |
C30B
11/003 (20130101); C30B 29/40 (20130101); C30B
29/42 (20130101); Y10T 117/1088 (20150115); Y10T
117/1076 (20150115); Y10T 117/1068 (20150115) |
Current International
Class: |
C30B
11/00 (20060101); C30B 011/00 (); C30B
029/42 () |
Field of
Search: |
;151/222,217,219,83
;164/122,122.1,122.2,123 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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33 23 896 |
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Jan 1985 |
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DE |
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38 39 970 |
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May 1990 |
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DE |
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0 887442 |
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Dec 1998 |
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EP |
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939146 |
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Sep 1999 |
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EP |
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102 03 891 |
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Apr 1998 |
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JP |
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Other References
Althaus et al., "Some new design features for vertical Bridgman
furnaces and the investigation of small angle grain boundries
developed during VB growth of GaAs.", Journal of Crystal Growth 166
(1996) p. 566-571..
|
Primary Examiner: Norton; Nadine G.
Assistant Examiner: Song; Matthew
Attorney, Agent or Firm: Neuner; George W. Edwards &
Angell, LLP
Claims
What is claimed is:
1. A device for producing a monocrystal by growing the monocrystal
from a melt of raw materials with a heating appliance for
generating a temperature gradient within the melt of raw material,
wherein the heating appliance comprises a rotationally symmetrical
furnace with a rotation axis (M) and with an essentially level
floor heater and an essentially level cover heater that can be
controlled to different temperatures, the device further
comprising: an insulating device that is structured and arranged in
such a way that a heat flow in a radial direction perpendicular to
the rotation axis (M) of the furnace can be controlled at a preset
rate.
2. A device in accord with claim 1, wherein the insulating device
is further structured and arranged to provide an insulating effect
having a gradient from the cover heater to the floor heater.
3. A device in accord with claim 1, wherein the furnace is
cylindrical and further comprising a controller to control a
temperature of the floor heater to be lower than a temperature of
the cover heater.
4. A device in accord with claim 3, wherein the controller can
lower the temperature of the floor heater continuously with
reference to the cover heater.
5. A device in accord with claim 1, wherein the insulating device
has a tapered cone body with a coaxial cylindrical hollow space
that is open at the top and bottom, the insulating device being
positioned in the furnace so that the tapered end is towards the
floor heater.
6. A device in accord with claim 1, further comprising a jacket
heater for the furnace.
7. A device in accord with claim 1, further comprising a heat
transmission part having a rotationally symmetrical profiled or
unprofiled shape.
8. A device in accord with claim 1, wherein the heaters comprise a
heating surface having a ratio to a surface of a monocrystal to be
produced to provide a temperature that is essentially homogeneous
over a radial cross-section of the monocrystal and a temperature
gradient between the floor heater and the cover heater that is
essentially constant.
9. A device in accord with claim 8, wherein the surface of each
heater is at least 1.5 times the cross-sectional area of the
monocrystal.
10. A device in accord with claim 1, the device further comprising
a clearance between the floor heater and the cover heater, the
clearance being greater than the length of a monocrystal to be
produced.
11. A device in accord with claim 1, wherein said insulating device
comprises graphite.
12. A device in accord with claim 1, further comprising a crucible
for receiving the melt of raw material, the crucible being located
between the floor heater and the cover heater.
13. A device in accord with claim 1, wherein the furnace is
cylindrical and further comprising: a controller to control a
temperature of the floor heater to be lower than a temperature of
the cover heater; an insulator device having a tapered cone body
with a coaxial cylindrical hollow space that is open at the top and
bottom, the insulator device being positioned in the furnace so
that the tapered end is towards the floor heater; a jacket heater
for the furnace; a crucible for receiving the melt of raw material,
the crucible being located between the floor heater and the cover
heater; and a clearance between the floor heater and the cover
heater, the clearance being greater than the length of a
monocrystal to be produced.
14. A device in accord with claim 13, further comprising a heat
transmission part having a rotationally symmetrical profiled or
unprofiled shape.
15. A device in accord with claim 14, wherein the floor and cover
heaters comprise a heating surface having a ratio to a surface of a
monocrystal to be produced to provide a temperature that is
essentially homogeneous over a radial cross-section of the
monocrystal and a temperature gradient between the floor heater and
the cover heater that is essentially constant.
16. A device in accord with claim 15, wherein the surface of each
of the floor and cover heaters is at least 1.5 times the
cross-sectional area of the monocrystal.
17. A device in accord with claim 13, wherein the controller can
lower the temperature of the floor heater continuously with
reference to the cover heater.
18. A device in accord with claim 13, wherein said insulating
device comprises graphite.
19. A device in accord with claim 1, wherein said insulting device
comprises graphite.
20. A device for producing a monocrystal by growing the monocrystal
from a melt of raw materials with a heating appliance for
generating a temperature gradient within the melt of raw material,
wherein the heating appliance comprises a rotationally symmetrical
furnace with a rotation axis (M) and with an essentially level
floor heater and an essentially level cover heater that can be
controlled to different temperatures, the device further
comprising: an insulating device that is structured and arranged to
provide an insulating effect having a gradient from the cover
heater to the floor heater.
21. A device in accord with claim 20, wherein the furnace is
cylindrical and further comprising a controller to control a
temperature of the floor heater to be lower than a temperature of
the cover heater.
22. A device in accord with claim 20, wherein the insulating device
has a tapered cone body with a coaxial cylindrical hollow space
that is open at the top and bottom, the insulator device being
positioned in the furnace so that the tapered end is towards the
floor heater.
23. A device in accord with claim 20, wherein the heaters comprise
a heating surface having a ratio to a surface of a monocrystal to
be produced to provide a temperature that is essentially
homogeneous over a radial cross-section of the monocrystal and a
temperature gradient between the floor heater and the cover heater
that is essentially constant.
24. A device in accord with claim 21, wherein the controller can
lower the temperature of the floor heater continuously with
reference to the cover heater.
25. A method for producing a monocrystal of a III-V composite
semiconductor material, said method comprising growing the
monocrystal in a device according to any one of claims 1 to 19.
26. A method for producing a monocrystal of gallium arsenide, said
method comprising growing the monocrystal in a device according to
any one of claims 1 to 19.
Description
The invention concerns a device for producing monocrystals. In
particular the invention concerns a device for producing
monocrystals of various materials, for example III-V materials, for
example of gallium arsenide monocrystals.
Familiar devices for producing monocrystals of various materials,
for example III-V materials, for example of gallium arsenide
monocrystals, generally comprise multiple temperature zone
furnaces, such as those described in DE-OS-38 39 97 and in U.S.
Pat. Nos. 4,086,424, 4,423,516 and 4,518,351.
These multiple temperature zone furnaces can consist not only of
metal heat conductors but also of heating conductors containing
carbon The so-called multiple zone tube furnaces enable a variable
structure of a temperature field suitable for crystal growth and
its displacement along the furnace's axis of rotation.
However, devices of this kind are characterized not only by an
axial but also by a radial heat flow that can lead to a variable
growth rate and to an unfavorable formation of the interphase
melt-crystal.
In addition, multizone or multiple temperature zone furnaces are
composed of a variety of thermal construction elements and this
requires considerable expense for dismantling and assembling for
maintenance work. As the number of zones increases the amount of
automation increases and with it the susceptibility to faults of
multizone furnaces.
In particular for the production of monocrystals with a large
diameter, for example 2", 3", 100 mm, 125 mm, 150 mm 200 mm and
above, there is the problem that a radial heat flow in the crystal
has an effect on the isotherms, i.e. on the interphase
melt-monocrystal in a vertical or axial direction respectively.
A device characterized by an insulating device being planned that
is designed in such a way that a heat flow in a radial direction
vertical to the rotation axis (M) of the furnace (1) can be
restricted to a preset rate and whereby the insulating device (6)
is designed so that its insulating effect is reduced from the cover
heater (3) to the floor heater (2) is familiar from the Journal of
Crystal Growth, NL, North-Holland Publishing Co. Amsterdam, Vol.
166, No. 1/4, Sep. 1, 1996, pages 566-571.
The task of the invention is to provide a device for producing
monocrystals, in particular monocrystals of various III-V
materials, for example from gallium arsenide, in which the heat
control is almost exclusively axial.
The task is solved by means of a device for producing a monocrystal
by growing from a melt of raw materials of the monocrystal to be
produced with a heating appliance (1) for generating a temperature
gradient within the melt of raw material whereby the heating
appliance (1) has a rotationally symmetrical furnace (1) with a
rotation axis (M) and with an essentially level floor heater (2)
and an essentially level cover heater (3) that can be controlled to
different temperatures and characterized by an insulating device
being planned that is designed in such a way that a heat flow in a
radial direction vertical to the rotation axis (M) of the furnace
(1) can be restricted to a preset rate and whereby the insulating
device (6) is designed so that its insulating effect is reduced
from the cover heater (3) to the floor heater (2).
In certain preferred embodiments of the invention, the device has a
furnace designed cylindrically and a controller that is designed in
such a way that the temperature of the floor heater (2) can be
reduced in comparison with the temperature of the cover heater. In
other preferred embodiments, the device has an insulator device (6)
that is designed as a tapered cone body with a coaxial cylindrical
hollow space that is open at the top and bottom and placed in the
furnace (1) in such a way that the tapered end is towards the floor
heater (2). Preferably, the insulator device is made, for example,
of graphite. In other preferred embodiments, the device comprises a
furnace (1) having a jacket heater (5). In still other preferred
embodiments, the device comprises a heat transmission part (6)
having a rotationally symmetrical profiled or unprofiled shape. In
yet other preferred embodiments, the device includes a heating
surface of the heaters being calculated in a ratio to the diameter
of the monocrystal to be produced so that a temperature that is
essentially homogeneous over the radial cross-section surface of
the monocrystal to be produced can be generated together with a
temperature gradient between the first heater (2) and the second
heater (3) that is essentially homogeneous and constant.
Preferably, the size of the surface of each heater (2, 3) is at
least 1.5 times the cross-sectional area of the monocrystal to be
produced is calculated. Preferably, the controller is designed so
that the temperature of the first level heater (2) can be lowered
continuously as against the second level heater (3). In still other
preferred embodiments, the clearance between the heaters is greater
than the length of the monocrystal to be produced. In yet further
preferred embodiments, a crucible (4) for receiving a melt of raw
material of the monocrystal to be produced is provided between the
first heater (2) and the second heater (3). Preferred devices of
the present invention are particularly suited for the production of
a monocrystal from a III-V composite semiconductor, for example, a
monocrystal of gallium arsenide.
The device has the advantage that a homogeneous axial heat flow is
guaranteed and that practically no heat at all can run off in a
radial direction, i.e. of a radially homogeneous temperature at the
upper and lower heating plates and the intermediate sections.
Other elements and expediencies can be seen in the description of a
design example by means of FIG. 1.
The FIGURE shows a schematic cross-section view of the device
according to the invention with an axis of rotation M extending
vertically.
The device for producing monocrystals has a cylinder-shaped furnace
1 with a lower heating plate as the floor heater 2 and an upper
heating plate as the cover heater 3. The high-temperature heat
conducting plates (e.g. CFC) have a circular cross-section. The
diameter of the floor heater 2 and of the cover heater 3 is not
less than 1.5 to 2 times the diameter of the crystal to be
produced, so that there are no radial heat flows in the system that
are caused among other things through the non-rotationally
symmetrical influences of the current supply. The clearance between
floor heater 2 and cover heater 3 is dimensioned so that a crucible
4 for the crystal growth can be located between them.
A control appliance that is not shown is planned with which floor
heater 2 and cover heater 3 can be triggered in such a way that
cover heater 3 can be kept roughly at the melting temperature of
the material to be processed and floor heater 2 can be kept at a
slightly lower temperature. The controller is in addition designed
so that the temperature of floor heater 2 can be continuously
reduced in the growth process in comparison with the temperature of
the cover heater, so that the melt of the raw material in the
crucible 4 can harden continuously from bottom to top.
The cylindrical furnace 1 has in addition a jacket heater 5 that is
formed for example in the cylindrical boundary wall of the furnace.
There is a control appliance planned that is designed so that the
jacket heater 5 can be held at a temperature in the proximity of
the melting point of the raw material in the crucible.
To prevent a flow of heat in a radial direction the furnace 1 has
in addition a rotationally symmetrical insulator 6 made of
heat-insulation material. Insulator 6 has the shape of a tapered
body with a coaxial cylindrical interior that is open at the top
and the bottom. The outer wall 7 of the insulator 6 is therefore
shaped like a truncated cone and the inside wall 8 is shaped like a
cylinder. Insulator 6 is arranged in the furnace in such a way that
the tapered end 8 is in the direction of floor heater 2 and the end
opposite to the tapered end is in the direction of cover heater 3.
The inside diameter of the insulator is greater than the diameter
of the crucible 4 that is to be inserted. The insulator is made
preferably of graphite. The hollow truncated cone shape of the heat
conducting profile 6 results in a free radiation space 9 between
the heat conducting profile and the jacket heater 5 that
contributes to the azimuthal compensation of the temperature
through the main heater.
The design and arrangement of insulator 6 in the furnace 1
described above brings about a reduction in the heat insulation
moving from the cover heater 3 to the floor heater 2 in a radial
direction between a melt of raw material in crucible 4 and the
jacket heater 5.
For operational purposes the crucible 4, which contains the crystal
nucleus is placed into the furnace. Boroxide B.sub.2 O.sub.3 and
polycrystalline gallium arsenide are then added. The jacket heater
5 is then triggered in such a way that it is brought to a
temperature that is sufficient to heat the reaction space to the
working temperature and to melt the solid feedstock material. The
added polycrystalline gallium arsenide is melted so that it forms a
gallium arsenide melt 10 and is covered by a covering melt 11 made
of molten B.sub.2 O.sub.3 so that contact of the gallium arsenide
with the crucible wall is prevented.
The growing process is then carried out as follows. The cover
heater 3 is brought to a temperature of approx. 1300.degree. C. and
the floor heater 2 is brought to a temperature of approx.
1200.degree. C. A temperature gradient is formed between the cover
heater 3 and the floor heater 2 that is practically the temperature
gradient that is found between two infinite parallel level plates.
The temperature of the floor heater is then reduced continuously so
that the melt 11 in the crucible 4 crystallizes out evenly from
bottom to top. By controlling and/or regulating the temperature of
the floor heater 2 relative to the temperature of the cover heater
3 it is possible to move the vertical position of the melt
isotherms between the two heaters and therefore to control the
crystallization. The jacket heater must be corrected slightly
throughout the process time to maintain the ideal axial
temperature, because the system's overall energy level is reduced,
and to ensure that the radial losses, that are compensated for
through the jacket heater, are reduced.
The jacket heater 5 serves to compensate global heat losses and to
prevent a radial heat flow. Through insulator 6 a high level of
insulation is achieved in the area of cover heater 3 in a radial
direction and a lower level of insulation in the area of floor
heater 2 in a radial direction. This guarantees an axial heat flow
parallel to the rotation axis of the furnace during the
crystallization process.
During the crystallization process and thereafter isotherm
formation in the reaction vessel is in this way possible in any
form. The isotherm form that is aimed for can be displaced through
the strictly axial heat flow over the complete height of the
reaction space between cover heater 3 and floor heater 2. The
device in accordance with the invention enables the production of
monocrystal of different III-V materials with large diameters, such
as for example gallium arsenide with a diameter of 2", 3", 100 mm,
125 mm, 150 mm 200 mm and larger.
Depending on the monocrystal that is to be produced, for example in
regard of its material or its diameter, the insulator 6 may be
designed as a hollow cylinder. The aim is simply to guarantee a
strictly axial heat flow and to prevent the heat flowing off in a
radial direction. In this way the target can be reached of
obtaining a constant rate of crystal growth per time unit.
In a modified form the heat transmission cylinder 6 is not in the
shape of a tapered cone but is shaped so that a desired axial
isotherm course is achieved. Any particular form is conceivable
here and is calculated by means of the desired isotherm course. Any
type of desired heat flow can be designed through the form of the
material and the type of the material. In this way the target can
be reached of obtaining a constant rate of crystal growth per time
unit.
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